Fix plant coincident sizing logic problem

[EnergyArchmage]

Pull request overview

This PR is for issue #5665. The logic checking for valid timestamps would not allow for sizing with a valid max demand timestamp and an invalid max flow rate timestamps. Changed a "||" to an "&&" and added some robustness checks.

Added unit test to test the condition with a null flow timestamp.

Note that the presence of null timestamps that need to be checked has been corrected by #5751 , making this issue somewhat moot.

Work Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• Title of PR should be user-synopsis style (clearly understandable in a standalone changelog context)

Review Checklist

This will not be exhaustively relevant to every PR.

• Code style (parentheses padding, variable names)
• Functional code review (it has to work!)
• If defect, results of running current develop vs this branch should exhibit the fix
• CI status: all green or justified
• Performance: CI Linux results include performance check -- verify this
• Unit Test(s)
• C++ checks:
  • Argument types
  • If any virtual classes, ensure virtual destructor included, other things

[nrel-bot-3]

@EnergyArchmage @lgentile it has been 14 days since this pull request was last updated.

[mjwitte]

@EnergyArchmage Is there a defect file that shows this bug?

[mjwitte]

Looks good. Will merge after CI reports back.